Polymerization of vinyl acetate initiated by 2,2'-azobis(isobutyronitrile) at 75 degrees C in the presence of iodine has been investigated. The process efficiently controls the number-average molecular weight and low polydispersities (Mw/Mn = 1.52). Poly(vinyl acetate) with predetermined molecular weight and relatively low polydispersity was successfully synthesized. The polymerization was followed by online 1H-NMR spectra to investigate the evolution of several compounds in the reaction medium, especially the adduct of a-iodoisobutyronitrile ((CH3)2(CN)C?I) between primary radicals and iodine. The structure of the end groups of poly(vinyl acetate) also was investigated using 1H-NMR spectra. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012